The Netherlands midfielder has been missing for much of Liverpool's dismal run of results due to injury, but Slot has confirmed he trained yesterday and is in training today.
Liverpool face Villa having lost six of their past seven games in all competitions - including the midweek Carabao Cup home defeat to Crystal Palace.
Slot began at his media conference with an update on Gravenberch: "Ryan trained yesterday and with us today and we'll make the call if he can start.
"I am happy with the team, the quality we have and convinced by the strategy and policy we have. But that makes it the issue, not all of them had a proper pre-season or have been injured, so when three of four are injured you go back to 15 or 16.
"I am convinced 20 is enough but we are struggling to keep them fit for obvious reasons."
Asked about the form of Alexander Isak, Slot said: "Alex came to us September 1st and it has been harder to keep them fit, so if a few aren't available it comes to the same players. Maybe last season we were lucky and now unlucky? But we've had a few away games with only a few days rest in between. No excuses, before people say...
"We have to manage the situation, three games in seven or eight days. So nothing to do with squad depth more just injuries and availability of players."
Not time to reflect
Asked if he has learned anything about himself during this losing run, Slot insists now isn't the time to consider such lessons.
"Maybe learning comes later," he told reporters. "(I'm) mainly focused on how I can change and evaluate the decisions made afterwards. My focus isn't looking back but how can we get a good performance on Saturday.
"The learning part comes later, the focus is on the future and is on how we can get a good result and performance versus Villa."
Asked if he can pinpoint reasons for their sudden slide, Slot said: "I think first half versus Palace was similar to 60 mins versus Brentford.
"The quality of the players gives me confidence and the chances we create, it will eventually lead to these players scoring more. We have to address certain other things.
"If I speak about what we have to improve, people say I am making excuses. A lot of positives to go into this weekend and the amount of chances we create is still good enough for the competitions we want to compete for."
Quizzed about whether his players can physically compete in the Premier League, Slot admits their defending has fallen short so far this season.
"It gets more important in every Premier League game, never helpful ending with a set piece versus United, conceding and concede another one from a throw in straight away. We defended 16 set pieces and 15 we defended well but we are at this moment where 15 isn't enough.
"Someone said to me, who works in a different department: 'No plan survives the first contact' and that is what makes it tough five mins and you're a goal down.
"Never good for confidence. If I liked a bit of Brentford it was after we conceded, we created our chances, couldn't score. Last 10 minutes it became more of their game."
Defending long balls
Asked to expand on last week's admission they're struggling against direct football, Slot concedes opposition managers are perfecting a way to target Liverpool's defence.
He said: "They are really good at that. Chelsea played their own game against us and we didn't win that one either. When people ask me why it was difficult and I try to explain why.
"People don't ask me can I come up with excuses and then I give an answer. I underestimate a lot of analysts throughout the country, if you ask me why it is tough, to say this without opening the eyes of upcoming opponents.
"These two teams (Villa and Manchester City) bring it out from the back more (than long balls) but they are very good at it. Villa beat City via a set piece."
Indeed, Villa go into the clash having beaten Manchester City last weekend.
Asked what he expects from Villa tomorrow, Slot said: "If you don't win at the beginning, people say it's not the same team and you win and then it's positive again. With us it's the opposite. Most are around the same points apart from Arsenal so it says the Premier League is tough.
"You can see the signs of Villa, playing style is really good. Villa didn't make a habit of (losing games)."
Contract talks
Slot was taken aback when asked about his contract and if talks over a new deal had commenced.
Slot's deal runs to 2027, and he said: "This is the last question that I was expecting. My focus is completley on getting Liverpool back to winning ways.
"That is my first answer and my second answer, contract talks, if they are even there, we never speak about this here.
"Let us first start to win again, that is my main focus."